The present invention relates to a method and device for guiding the leader of the web in the drying section of a paper machine.
The invention relates to a method of guiding the leader of the web in the drying section of a paper machine. In this method, a narrow leader is cut out of a full-width web by water jets or the equivalent, against a roller of the press section, for example. The leader is guided by air jets into the gap between the threading ropes and is carried between the threading ropes over the drying cylinders.
The invention also relates to a device for undertaking the method of the invention, which device is provided after the press section of the paper machine at the initial end of the drying section. The device comprises blowing means by which the leader of the web is guided and a pair or group of threading ropes, running in guide grooves formed in an extension of the mantles of the drying cylinders.
As is known in the prior art, when a paper machine is started or after a break of the web, the end of the web is threaded through the drying section by cutting a narrow leader strip out of the web against a rock roller, for example, by a water jet. The leader has a width of about 200 mm and is threaded manually to the threading devices by air jets. As is known in the prior art, the threading devices in the drying section of a paper machine comprise pairs of ropes, each drying group being provided with ropes running over pulleys placed in connection with the ends of the drying cylinders. Usually, the leader is guided between two ropes, an outer and an inner rope, but in some paper machines three jointly operative ropes are used.
The constant increase in the running speeds of paper machines has resulted in increasing difficulties in the threading of the end of the web. The maximum difficulties occur right after the press section and in the initial drying section, as well as in the zones between drying groups.
When prior art threading arrangements are used, the leader must be guided manually at several points in the drying section by air jets placed at the ends of hoses. This work is very dangerous, because it must be performed in immediate proximity to revolving massive components. Furthermore, the operator must be well accustomed to the work and have good professional skill in order to adequately do the work.